The frame sizes used by networked computing devices to transmit and/or receive data are network-dependent, and in some cases they increasing over time. For an example of increasing size, the latest Ethernet network interface cards (“NIC”), which are operable at one or more gigabits per second (“Gbps”), now include physical (“PHY”) and media access control (“MAC”) components that can also communicate data at frame sizes larger than the traditional (standardized) maximum frame size (i.e., 1522 bytes). One such larger frame size is the jumbo frame size of 9,022 bytes, which is typically used in gigabit Ethernet networks.
But standards that govern these larger frame sizes do not currently exist. For example, the size of an Ethernet jumbo frame is not standardized. According to the Institute of Electrical and Electronics Engineers (“IEEE”) standard IEEE 802.3-2002, frame sizes larger than 1522 bytes are not allowed. Further, there generally is no other accepted industry standard for harmonizing Ethernet jumbo frame sizes. As such, various vendors tend to manufacture network devices with differing jumbo frame size capabilities, such as 4,470 bytes, 9,018 bytes, 16,406 bytes, etc.
The lack of an Ethernet jumbo frame standard has slowed adoption of jumbo frames for use in Ethernet networks. Network administrators have long resisted mixing network elements that support varying frame sizes in the same network, such as within a single local area network (“LAN”). In practice, legacy switches and repeaters tend to interpret any frame size over 1522 bytes as an illegal condition, thus curtailing the propagation of such frames. Consequently, many vendors and users recommend upgrading all of the network elements of a given subnetwork or a network to support jumbo frames, if jumbo frames are to be deployed within an Ethernet network. This ensures that these frames can be used safely, without causing such error conditions. As massive upgrades in network elements are costly, replacement of network devices is generally done incrementally rather than at one time. Even if some legacy Ethernet devices are replaced with jumbo-capable network elements, the remaining legacy network elements in the network limit the maximum data transmission format in the portion of the network to which they provide connectivity. Consequently, network managers routinely disable the jumbo frame capabilities of jumbo-capable network elements when introduced into an existing network. Then, the frame sizes of these devices are set to match those of the legacy equipment. These actions typically lead to negligible or nonexistent use of jumbo frame traffic over networks. Ethernets are also frequently connected to other network types, which may have different maximum frame sizes, via layer-2 bridges (also known as switches). Two examples of such situations are wireless IEEE 802.11 Access Points (the IEEE 802.11 standard supports frames up to 2346 bytes in length), and FDDI-to-Ethernet switches (since FDDI supported frames up to 4500 bytes in length). The addition of jumbo frame capability to certain Ethernet devices has introduced variability of the maximum supported frame size even in pure Ethernet environments. Due to the existence of multi-LAN bridges, and of Ethernet jumbo frames, there was a need for an MTU discovery technique, such as is described by this invention.
Thus, there is a need for a method and/or an apparatus to facilitate the use of frame sizes that are larger than those commonly used over a network, especially where the network may include some network elements capable of supporting mixed frame sizes.